DICELLOGRAPTUS. 



1 15 



Figs. 88 a, b, and c. —Dicellograptus divaricati 

 rigidus, Lapw. 



aperture of the third theca. This film 

 gives a very thickened appearance to 

 the axillary portion. 



Specimens in which this chitinous 

 web is preserved rarely show the form 

 of the thecas ; but from other examples 

 it is clear that they are essentially similar 

 to those of the typical species, though 

 they are somewhat more distant (eight 

 in 10 mm.). 



Affinities. — Var. rigidus is easily dis- 

 tinguished from all other Dicellograpli 

 belonging to this group by the uniform 

 width, stoutness, and rigidity of its 

 stipes. 

 Horizon and Localities. — Glenkiln and (?) Lower Hartfell (zone of Glimacog. 



WilsOill). 



S. Scotland: Birnock Water; Wanlock Head; Dobb's Linn, etc. Ireland: 

 Ballygrot. 



Associates. — Var. rigidus occurs in the Glenkiln Shales associated with Didymog. 

 superstes, Dicellog. sextans, Gryptog. tricornis, etc. It has also been quoted from 

 the zone of Glimacog. Wilsoni. The best specimens are in the collections of 

 Lapworth and the Sedgwick Museum. 



a. Proximal end without " web." Enlargement of 



part of PI. XX, fig. G e. 



b. Proximal end with " web." Enlargement of counter- 



part of PI. XX, fig. 6 b. 



c. Distal thecal. Enlargement of part of PL XX, fig. 6 a. 



Var. salopiensis, var. nov. Plate XX, figs. 7 a — e. 



Pigs. 89 a and b. — Dicellograplus 

 divaricatus var. salopiensis, nov. 



\ 



jfP 



a. Proximal 



of part 



b More distal t 



rnentof pari 



l 



Another variety of D. divaricatus is found in the 

 Glenkiln Beds of Shropshire and of S. Scotland. 

 It is characterised by its slender stipes, which have 

 throughout their extent a uniform width of - 5 mm. 

 only. The thecas are of the same general type as 

 those of D. divaricatus, and number twelve to ten in 

 10 mm. 



Affinities. — Var. salopiensis is distinguished from the 

 other members of the group of D. divaricatus by its 

 slender stipes, and from D. pumilus and D. exilis, which 

 it resembles somewhat in shape, by the character of its 

 thecal 



Horizon mid I, aridities. — Llandeilo (" Ga nograptus " 

 beds, above the Llandeilo Limestone), Glenkiln Shales. 



